1. Field of the Invention
The present invention generally relates to an ISDN (Integrated Services Digital Network), and more particularly to an ISDN line circuit monitor system for monitoring messages transferred between a network and terminals accommodated in the network.
2. Description of the Related Art
As is well known, an ISDN uses a complex protocol defined between each terminal and a network. Such a complex protocol is different from a protocol used in a conventional telephone network. Since the protocol used in the ISDN is complex, there is a possibility that a protocol mismatch may take place, so that a terminal cannot be connected to a network or additional services cannot be used.
In order to detect such a protocol mismatch, it is necessary to store messages, which are actually transferred between the terminal and the network, and to analyze the messages. For this purpose, a conventional ISDN has monitor equipment which monitors the contents of a D channel when a line switching terminal is used, the contents of the D channel when a D channel packet is used, and the contents of a B channel when a B channel packet is used.
Since B and D channels (two 64 kbps B channels and one 16 kbps D channel) are time-division-multiplexed on each subscriber line circuit, a monitor terminal of the monitor equipment must be connected to a specific part of a hardware structure of an exchange at which the B and D channels have been separated from each other. However, it is necessary to draw a related package of the hardware structure of the exchange from a shelf in order to connect the above-mentioned monitor terminal to the related package. During this operation, the exchange services to subscribers related to the drawn package are stopped.
Further, there is a possibility that the monitor terminal may be mistakenly connected to an unwanted circuit portion since the above operation is very complicated. Furthermore, when a remote line concentration unit is used, it is necessary to bring the monitor equipment to the remote line concentration unit in order to monitor the messages between the terminal to be monitored and the network.